Lamp making method



March 10,1942. c. A. LAlSE 2,216,048

LAMP MAKING METHOD Original Filed March 23, 1955 l l l' I l I i'g12w. /0,Z v/ &2. a 2 v 5 a Q: I

. INVENTOR CLEMENS ALNSE DECEASED av FIDELITY umou TRUST dompmv Ado "7M6TIME RUDOLPH SIEVERT, ExEcuTo RS ATTORN.

. the lamp construction.

Patented Mar. 10, 1942 LAMP MAKING METHOD Clemens A. Laise, deceased,late of 'lenafly, N. 1., by Fidelity Union Trust Company, Newark, N. J.,and Rudolph Sievert, Weehawken Township Hudson County, N. J., executors,assignor to Callite Tungsten Corporation, Union City, N. J., acorporation of Delaware Original application March 23, 1935, Serial No.

1939, Serial No. 277,944

1 Claim.

This invention relates generally to improvement in high efiiciencyincandescent lamps, and especially to lamps of the character thatutilize metallic filaments as light emitting elements. An importantfeature of the invention concerns a novel electrical circuit, preferablyembodied in the lamp structure itself, which is adapted to produce ahigher efliciency combined with longer life than is possible to attainwith the lamps of the art' as heretofore known. The invention-isparticularly concerned with the construction of such a. lamp and circuitand method of making the same, which is especially well adapted for usein lamps produced in conformity with the principles herein set forth. f

This application is a division of United States Patent No. 2,214,742,issued September 17, 1940.

The expression "high efficiency lamp as used in the present applicationneeds a certain definition. It is probably true that this term has beenin use since the early days of the lamp 'art.

of metallic filaments, the lamps utilizing these filaments became knownas high eiliciency lamps. The term, however, had meaning only incomparison with carbon lamps and other lamps of lesser efficiency. Withthe appearance of the tungsten filament lamp, the term acquired a newmeaning and when this was followed by the gas-filled lamp with a coiledtungsten filament, it was'thought that a lamp of this type was the highefli'ciency lamp."

Developments of recent years, however, have shown still higheremciencies are possible. For, whereas in 'formertimes each increase inemciency was attained by 'use of an improved filament material or by useof a more suitable gaseous atmosphere, it has lately been the aim to usethe same gaseous atmosphere and the same filament material but to attaingreater efliciency by applying more exact engineering principles toDivided and this application June 7,

creases. There is, therefore, at the instant of switching on, a suddensurge of current through thefilament which produces a shock sufilcientin many cases to rupture the filament.

It is an object of the present invention to provide a lamp capable ofattaining the highest possible emciency and which at the same time willbe capable of preventing the surge and consequent shock due to theswitching on of the current.

It is a further object of the invention to provide a lamp of thehighefliciency described that will have a long commercial life. Theelimination of the initial surge, of course, is the pri- It is certainlytrue that with the introduction In the lamp art, efliciency consists inobtain-'- ing the greatest amount of lumens per watt consistent with asufficiently long life to satisfy commercial and practical needs. Asefiiciency is increased, the life ofthe lamp is shortened, other thingsbeing equal. In the-lampart of thepast, however, the highest possibleefliciency was rarely attained for the reason that such a lamp was notwell adapted to sustain the shock of turning the current on or off. Ametal filament is most conductive when coldybut as the mary reason forthis longer life, not only because -with the elimination of the surgethe shock is leads and the concomitant destruction of the filament atthe point -of junction with the leads.

It is a still-further object to provide a lamp of .high efliciencyhavinglead wires of small diameter and hence with only slight cooling effectupon the filament. In lamps of the present art, the cooling effect ofthe leads is sufficient to cause relatively largedifierences intemperature with the highest temperatures midway between the leads. Whensuchdifl'erences of temperature exist, the filament frequently rupturesor fuses at the exceedingly hot midway point.

To accomplish these objects of the invention, aspecially designedcircuit is provided in the lamp.

The preferred elements of the circuit above suggested comprise afilament of the physical and mechanical structure hereinafter described;a resistance element having resistance characteristics opposed to thoseof the filament and sumcient to balance the initial current surge;

and leads of small diameter and high conductivity. Such a circuit isrepresented diagrammatically in Fig. 1 of the annexed drawing. In Figs.2 and 2 are illustrated cross-sectional and longitudinal sectional viewsof the filament;

temperature increases, the resistance also in- 56 the circuit andfilament may be incorporated in a standard type of lamp; Fig; 5 shows acurrent-time curve of the initial operation of'an ordinary lamp; andFig. 6 shows the currenttime curve of a lamp constructed in accordancewith the invention; Fig. 7 is an .enlarged section taken along the line1 1 of Fig. 3 showing the construction of the lead wires.

The above described elements will be described seriatim. First, thefilament. The filament of the lamp of this invention may be of thegeneral type described and claimed in Patent No. 1,631,- 493, consistingof tungsten as a base with additions of boron nitride or boron-suboxideand potassium borate which have a scavenging efiect.

The metallic bar from which the filament is drawn is so treated that atthe sintering or metallizing temperature a portion of the scavengersdistils out and takes along with it detrimental impurities that may bepresent in the tungsten base. The amount of such scavenger additions issuch that in the final filament the amounts remaining are very minute,being one-quarter of minimum, the filament has little tendency to twistor distort after it has been shaped and set into suitable concentratedform.

One prime cause of brittleness in tungsten filaments of the granulartype of the prior art,

is the presence of foreign non-metallic sub stances in the grainboundaries. For instance, in the old pressed or squirted tungstenfilaments, an organic binder was used which became carbonized during theprocess of manufacture and formed carbides in the crystal boundaries. Inthe drawn tungsten filament as first produced, additions of varioussubstances, such as the xides of calcium, aluminum or thorium, wereadded for the purpose of retarding the growth of crystals. This practiceresulted also in compounds in the grain boundaries that tended toproduce a brittle filament, particularly after a short period of use. Inthe later so-called nonsag tungsten filament additions are made to themetal that produce silicon compounds and probably also hydrides in the'grain boundaries with a resulting brittleness after relatively shortuse.

All such intergranular substances act solely as cements holding thegrains together and preventing the grains from coalescing and forminglarger grains. In the filament of the present invention, however, thecementing material is composed of scavenging substances which are addedto the tungsten powder from which the slugs are made and from which theyare drawn down to filament diameters. After the addition of thescavenging material to the powder, the same is worked into slugs in theusual way and the conditions of manufacture and heat treatment soregulated that they have a grain count of approximately 15,000 to 20,000grains per square millimeter.

The slugs are mechanically worked by swaging and drawing into wire andthen concentrated into coils or coiled-coils or rolled into ribbon andcorrugated or twisted into concentrated form. In making coiled coils offilament wire, the wire should be so wound that the magnetic effect dueto the line of force generated about it will not cause shortcircuiting.

When making coils or coiled-coils, mandrels of nickel or nichrome orother refractory metals soluble in acids may be used and the coil orcoiled-coil is heated on the mandrel preferably in an atmosphere of wethydrogen at temperatures ranging from 1000 C. to 1500 C. until apermanent set is imparted to the filament and the wire has been relievedof all of its strain. Thus, there will be no readjustment of the coilafter the mandrel is dissolved out.

Wet hydrogen is used, a practice contrary to that of the present art inwhich dry hydrogen is used in such operations, for the reason that wethydrogen tends to decompose carbides on the surface or in the grainboundaries of the filaments. If dry hydrogen is used, carbides arelikely to form with the filament metal in the presence of carbon orcarbon compounds. As a result of the process employing wet-hydrogen, thepliability and ductility of the filament is not impaired as it would beif dry hydrogen were used.

The heat treated coil and mandrel are then cut to proper lengths togivethe proper voltage of lamp and the mandrel is then dissolved in suitableacids such as nitric acid and sulphuric acid if nickel or nickel alloysare used as mandrel wire.

After the coil or other shape of filament treated in the above manner ismounted into the lamp, the lamp is sealed and exhausted or filled withgas and then flashed by connecting the lamp in series with a rheostat ornichrome resistance at about 125% over voltage,--that is, 125% of therated voltage of the filament for a period of about five minutes, sothat the filament quickly attains the germinating temperatures and thegrains coalesce or fiow into each other, producing a light emittingmedium with long interlocking sections which have little tendency to sagor distort. Such sections may consist of at least one turn'andpreferably several turns of coil, especially after the lamp has burnedabout one hour at its rated voltage.

During the flashing operation it is desirable to use twice the voltageof the greatest voltage of the lamp and so regulate the proper voltagein this temporary circuit so that about 125% drop takes place across thelamp and in the balance of the circuit consisting of a suitablerheostat.

During the heat treatment above described,

the scavenging materials tend to distil out, carrying with themsubstantially allimpurities, including occluded hydrogen, that may bepresent in the grain boundaries. With these impurities eliminated, thereis little obstruction to rapid grain growth and the formation in thefilament of long sections and but few interlocking section boundaries.Instead of the particular scavenging materials mentioned, otherrefractory nitrides may be used with excellent effect, such as tions ofa straight filament composed of interlocking sections 9 and 10, whichare representative of the filament structure above described.

It is apparent that this filament of few interlocking sections can beoperated at a much higher efficiency or lumen output and longer lifethan a highly crystallized filament of many grain boundaries.Furthermore, it retains its shape after it is once permanently set orflashed by the special process in the lamp circuit of this invention, sothat it does not droop, shrink, twist or short-circuit between theindividual sections.

The shape of the light emitting filament may be a round cylindrical wiresection, a square or oblong ribbon section, or may be in the form ofribbon corrugated or twisted or in the form of a coilora double coil orhelical coil.- For gasfilled lamps, especially of the higher voltagetype, a concentrated form such as'a coiled-coil is de-' sirable. Inevery case, however, the principle of treating the specially preparedfilament body remains the same, namely, that the filament body mentispreferably mounted upon lead wires of the general type described andclaimed in the patent to Clemens A. Laise andJacob Kurtz No.

2,120,561, dated June 14, 193 but the diameter.

of these lead wires, by virtue of the exceptional heat and currentconductivity characteristics of the material thereof, may be made muchsmaller than that generally used in lamps of the present art ofequivalent wattage andmay be as small as 50% of the cross-sectional areaof the lead wire of such generally used lamps.

The wire described and claimed in said Patent No. 2,120,561 may bedescribed generally as being composed of a nickel sheath and a coppercore, the nickel constituting a relatively large propor tion of thetotal wire and at least 10% thereof. In cross section such a wireappears as indicated in the enlarged view of Fig. 1.

A third and very important feature of the invention is that theresistance or ballast disposed in the circuit is incorporated in one ofthe leads either within the stem as indicated at l5-in Fig: 4, orwithout it as shown at l5.in Fig. 3; or it may even be arranged outsideof the lamp.

The purpose of this ballast or resistance is to eliminate the suddensurge of current through the lainp. It may consist. of a small chokecoil or similar device which momentarily has a high resistance'whenconnected across a difierence of potential and-then, as the currentbegins to flow, the resistance is practically eliminated so that theloss of power due to the presence of the same is practically negligible.

This coil or equivalent resistance may be imbedded, in metallic oxideand may or may not be enclosed in a ceramic, or resinous, or Bakelitecomposition which holds it in place and insulates it both electricallyand thermally. The conducting oxide may be iron oxide or otherequivalent oxide or conducting material which has a high current in thesame lamp when operating at its.

rated voltage. This is illustrated by the curves Fig. 5 which indicatethe initial surge of the lamps of the present art, and Fig. 6 whichindicate the initial performance of a lamp of the present invention.

The resistance or ballast is such that it does' not cause substantialloss of power in the circuit during the normal operation but merelydampens, reduces and tends to preventthe initial surge of current whenthe circuit. is first connected across a difierence in potential. Thiselimination of sudden surge of current prevents or retards the suddenrupture of filament at the grain boundaries and also reduces possibilityof arcing across the lead wires.

Figs. 5 and 6 above referred to are comparative curves with currentplotted against time showing the effect of the circuit of the presentinvention. In Fig. 5 the initial surge of current. introduced into anordinary'lamp is considerable but is quickly reduced to a constant valueafter a few seconds. In Fig. 6 the initial current introduced into alamp constructed in accordance with the principles of the presentinvention is shown to rise gradually to a constant value after a fewseconds said filament in said lamp at an over-voltage,

resistance when cold and becomes very conductive when heated upslightly.

The surge preventive inthe invention is placed directly into the circuitof theincandescent lamp either inside of the bulb, which is preferred,or

thereby bringing said filament instantaneously up to the germinatingtemperature of the grains and producing long sections of filament andinterlocking boundaries between said sections.

FIDELITY UNION TRUST COMPANY,

By L. G. McDOUALL,

